In the fabrication process of semiconductor devices such as a semiconductor integrated circuit on a semiconductor wafer, it is commonly practiced to divide the semiconductor wafer into individual chips by a dicing process.
Before applying such a dicing process, it is generally necessary to grind a surface of the wafer opposite a first surface on which the semiconductor devices are formed, such that the wafer has a predetermined thickness. For example, such a grinding process can be used to reduce the thickness of a wafer to 500 microns (μ) or less according to the specification of the semiconductor device.
In order to prevent damaging of the semiconductor wafer from, for example, cracking at the time of grinding, it is commonly practiced to protect the devices on the first surface, commonly referred to as the front side, of the wafer by an adhesive medium such as an adhesive tape. Generally, the adhesive tape used for such a purpose carries, on a tape support layer, a layer of adhesive material including acrylic resin with a thickness of about 30-40μ. The tape support layer, in turn, is formed of a polymer such as a polyolefin, polyvinyl, or polyethylene and generally has a thickness of about 100-150μ.
After the grinding process, the semiconductor wafer is diced into individual chips followed by removal of the adhesive tape. In order to help facilitate removal of the tape and adhesive, the adhesive layer used for such a purpose is generally added with a surfactant. By doing so, any adhesives remaining on the diced wafer surface or surfaces of the chips after tape removal can be more easily removed by cleaning with purified water or an organic solvent. It should be noted that the composition of adhesives used in such a tape changes substantially lot by lot, and the adhesive of the tape tends to establish very intimate adhesion with the wafer surface. Adhesive residues often remain, such as amorphous carbon, nitrides or amorphous polyimides, and extensive cleaning may be required. Such a strong adhesion suggests that there is a crosslink reaction between the adhesive and the residual materials on the wafer. Sometimes up to 60 minutes or more of cleaning time may be required. As the front side surface of the wafer generally includes a thin film, such as a polyimide or SiN, any tape adhesive remaining on the front side of the diced wafer surface or surfaces of the chips after tape removal, raises serious performance problems.
Attempts have been made to use an adhesive tape that carries a UV energy curable type adhesive on the tape base for the purpose of the protection of the wafer during the grinding process. When using such a UV energy curable type tape, an ultraviolet radiation is applied to the diced wafer covered by the tape, before removing (picking) the individual chips of the diced wafer from the tape, facilitating the removal of the tape. As the adhesive is cured by the ultraviolet radiation, the adhesion of the tape to the diced wafer is reduced substantially and removal of the individual chips from the tape is achieved more easily. If the UV energy curable type tape is not substantially fully cured because of insufficient UV energy delivered to the tape, adhesive residues can still remain on the chips originating from the diced wafer surface from which the tape was removed. One cause of insufficient UV energy delivery can be debris on the exposed tape surface blocking a portion of UV energy intended to be delivered to the tape. When UV light is used as the vehicle to deliver UV radiation to the tape, lamp or bulb problems can lead to insufficient UV energy being delivered to the tape. As a result, use of the UV energy curable tape has not been made a matter of common practice for fabricating semiconductor devices.
It is possible to eliminate the cleaning process by applying an ozone ashing process for a limited time interval against the front side surface of the diced chips after removal of the tape, such that any remaining organic materials are oxidized. However, such an ozone ashing process requires a huge facility investment and the cost of the semiconductor is therefore increased. It is also possible to apply an additional post treatment process by using an organic solvent, such as isopropyl alcohol, for removing any remaining adhesive residues. Such a post treatment inevitably lowers the production throughput of the semiconductor chips.
A UV energy curable tape that could be used to optically monitor the tape cure level and that could be used to optically determine when the tape was substantially fully cured and more easily removed from the diced wafer would be a substantial advance in semiconductor chip manufacturing technology.